Fur, Skin, and Ear Mites (Acariasis)

technical sheet

Classification flank. Animals with mite infestations have varying clinical External parasites signs ranging from none to mild alopecia to severe pruritus and ulcerative dermatitis. Signs tend to worsen Family as the animals age, but individual animals or strains may be more or less sensitive to clinical signs related Arachnida to infestation. Mite infestations are often asymptomatic, but may be pruritic, and animals may damage their skin Affected species by scratching. Damaged skin may become secondarily There are many species of mites that may affect the infected, leading to or worsening ulcerative dermatitis. species listed below. The list below illustrates the most Nude or hairless animals are not susceptible to fur mite commonly found mites, although other mites may be infestations. found. Humans are not subject to more than transient • Mice: Myocoptes musculinus, Myobia musculi, infestations with any of the above organisms, except Radfordia affinis for O. bacoti. Transient infestations by rodent mites may • Rats: Ornithonyssus bacoti*, Radfordia ensifera cause the formation of itchy, red, raised skin nodules. Since O. bacoti is indiscriminate in its feeding, it will • Guinea pigs: Chirodiscoides caviae, Trixacarus caviae* infest humans and may carry several blood-borne • Hamsters: Demodex aurati, Demodex criceti diseases from infected rats. Animals with O. bacoti • Gerbils: (very rare) infestations should be treated with caution. • Rabbits: Cheyletiella parasitivorax*, Psoroptes cuniculi Diagnosis * Zoonotic agents Fur mites are visible on the fur using stereomicroscopy and are commonly diagnosed by direct examination of Frequency the pelt or, with much less sensitivity, by examination Rare in laboratory guinea pigs and gerbils. Occasional of plucked tufts of fur. Follicle mites (Demodex spp.) in rabbits and rats. More common in mice. Almost are detected by light microscopic examination of skin universal in hamsters. Many of these mites are scrapings. Psoroptes cuniculi is detected by light commonly found in wild and pet populations of the microscopic evaluation of ear swabs, smeared onto above species. a microscope slide. Light microscopy is usually used to speciate mites, as morphology of claws and body Transmission shapes are keys to speciation. Mites may also be Mites are transmitted by direct contact with an infested diagnosed by euthanizing an animal and placing the animal or the environment of that animal (bedding, animal or its skin on paper in a Petri dish or plastic bag, incompletely cleaned cage). and then placing the sealed dish or bag in a cool place. Mites will then leave the animal to find a new host, and Clinical Signs and Lesions may be noted walking about on the paper. Rarely, mite eggs are ingested and found in the feces of the affected Fur mites live and breed on the fur, but descend to the animal. skin to insert their mouthparts for a meal of plasma or to feed on epidermal cells shed by the host. Skin mites Interference with Research live in the skin or hair follicles. Mites are commonly found on the dorsum of affected animals, specifically Animals with mites and severe clinical signs such as between the scapulae, on the head, on the neck, or the ulcerative dermatitis are not suitable for use in research. technical sheet

The zoonotic nature of some mites may also pose Thorough cleaning of all surfaces in contact with a health hazard to workers. Animals with inapparent animals should serve to remove mites from the mite infestations may still have sequelae that interfere environment, although the literature does not with research. For example, mice with Myobia musculi discuss susceptibility to cleaning agents. acariasis may have an increased IgE response, an increase in the formation of secondary amyloid, References hypoalbuminemia, and a decreased mean haemoglobin Baker DG. Natural Pathogens of Laboratory Animals: Their effects concentration. In hamsters, clinical signs are rarely on research. Washington, D.C.: ASM Press; 2003. 385 pp. associated with Demodex, and if seen, are usually Baker DG, editor. Flynn’s Parasites of Laboratory Animals. 2nd ed. related to advanced age or experimental manipulation. Ames: Blackwell Publishing; 2008. 813 pp.

Prevention and Treatment Fox JG, Anderson LC, Lowe FM, Quimby FW, editors. Laboratory Animal Medicine. 2nd ed. San Diego: Academic Press; 2002. Since mites are transmitted by direct contact with 1325 pp. infected animals, acariasis is prevented by quarantine (with adequate evaluation) or rederivation of all animals Fox J, Barthold S, Davisson M, Newcomer C, Quimby F, and entering the animal facility. Since animals with just Smith A editors. The Mouse in Biomedical Research: Diseases. 2nd ed. New York: Academic Press; 2007. 756 pp. a few mites may reinfest an entire facility, even after quarantine, many facilities quarantine and treat at the Percy DH, Barthold SW. Pathology of Laboratory Rodents and same time. Wild or pet animals may also carry mites, Rabbits. 3rd ed. Ames: Iowa State University Press; 2007. 325 pp. and excluding these animals from the animal facility is important.

Mites may be treated with a variety of compounds that vary in toxicity to the host. The most common treatments currently in use are ivermectin-family insecticides. Mite treatments are generally applied topically, although systemic treatments are described in the literature. Treatments may include an insecticide-permeated cotton ball placed in the cage, topical treatment of 1% ivermectin (oral sheep drench) between the scapulae, or 1% ivermectin diluted in water or water and proplylene glycol and sprayed on mice. The reader is advised to consult the literature or their veterinarian for further details. Newer ivermectins do not seem to be as effective as ivermectin. Care should be taken when treating transgenic mice, very young animals, or animals known to have blood-brain-barrier compromise. In many cases, treatment does not serve to eradicate the mites, and rederivation is used.

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